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Day 22: October 31, 2011 Pass Transistor Logic
ESE370: Circuit-Level Modeling, Design, and Optimization for Digital Systems Day 22: October 31, 2011 Pass Transistor Logic Penn ESE370 Fall DeHon
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Previously Penn ESE370 Fall DeHon
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Two Xor Gates Penn ESE370 Fall DeHon
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Today Pass Transistor Circuit Transmission gates Tristate gates
Output levels Cascading Series pass transistors? Delay Transmission gates Tristate gates Penn ESE370 Fall DeHon
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Cascading Pass Transistors
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Chain without Inverters
What if we did this? Penn ESE370 Fall DeHon
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Extract key path Penn ESE370 Fall DeHon
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t=0 (after Vin transition 10)
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t=4t (after Vin transition 10)
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t=∞ (after Vin transition 10)
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Focus on Pass tr Vgs? Operation mode? Current flow?
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Voltage of Chain What is voltage at output?
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How compare Compare Penn ESE370 Fall DeHon
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DC Analysis Penn ESE370 Fall DeHon
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DC Analysis – chain of 6 Penn ESE370 Fall DeHon
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Conclude Can chain any number of pass transistors and only drop a single Vth Penn ESE370 Fall DeHon
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Capacitance What is Capacitance per stage (@y)?
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Delay Delay as a function of chain length?
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Compare CMOS Buffered Pass TR Unbuffered Pass TR Delay Area
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Pass TR Tree What if we did this? Penn ESE370 Fall DeHon
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Path What’s different about this? Penn ESE370 Fall DeHon
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Gate Cascade? What are voltages? Penn ESE370 Fall DeHon
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Demonstration Circuit
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SPICE TODO show spice results of voltages
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Demonstration Chain Penn ESE370 Fall DeHon
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Spice Penn ESE370 Fall DeHon
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Conclude Cannot cascade degraded inputs into gates.
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Pass Rail-to-Rail Penn ESE370 Fall DeHon
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Transmission Gate Penn ESE370 Fall DeHon
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Bus Drivers Penn ESE370 Fall DeHon
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Tristate Driver Penn ESE370 Fall DeHon
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Tri-State Drivers
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Admin Project Midterm 2: Nov. 9th Due Friday
Week from today in the evening Penn ESE370 Fall DeHon
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Midterm Topics Scaling Logic Tau-model Elmore-delay No clocking
Estimation and optimization Elmore-delay Energy and power Logic CMOS Ratioed Pass transistor No clocking Except to motivate delay targets and power calculations Note: 2010 midterm Q4 – Cdiff, trans gates, Elmore, opt. Penn ESE370 Fall DeHon
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Idea There are other circuit disciplines
Can use pass transistors for logic Even chains of pass transistors Sometimes gives area or delay win Do not cascade as easily as CMOS Penn ESE370 Fall DeHon
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